Effect of CO2 Flooding on the Wettability Evolution of Sand-Stone

Wettability is one of the main parameters controlling CO2 injectivity and the movement of CO2 plume during geological CO2 sequestration. Despite significant research efforts, there is still a high uncertainty associated with the wettability of CO2/brine/rock systems and how they evolve with CO2 exposure. This study, therefore, aims to measure the contact angle of sandstone samples with varying clay content before and after laboratory core flooding at different reservoir pressures, of 10 MPa and 15 MPa, and a temperature of 323 K. The samples’ microstructural changes are also assessed to investigate any potential alteration in the samples’ structure due to carbonated water exposure. The results show that the advancing and receding contact angles increased with the increasing pressure for both the Berea and Bandera Gray samples. Moreover, the results indicate that Bandera Gray sandstone has a higher contact angle. The sandstones also turn slightly more hydrophobic after core flooding, indicating that the sandstones become more CO2-wet after CO2 injection. These results suggest that CO2 flooding leads to an increase in the CO2-wettability of sandstone, and thus an increase in vertical CO2 plume migration and solubility trapping, and a reduction in the residual trapping capacity, especially when extrapolated to more prolonged field-scale injection and exposure times.

Impacts of NO2 Impurities on the Indigenous Microbial Community Structure and Diversity in CO2-Saline-Sandstone Interaction System

Laboratory experiments (150 days) were performed to analyze the influence of NO2 impurities on indigenous microbial communities and diversity with 16S rRNA sequence at real GCS site (Geological CO2 Sequestration, ordos, China) conditions (pressure: 15 MPa, temperature: 55 °C). The possible impact of metabolic activity on the GCS process was investigated through the BLASTn search. Compared with the pure CO2, results demonstrate that the biomass and biodiversity were lower, due to the lower pH, within 60 days after the co-injection of 0.1% NO2. Subsequently, the pH was quickly buffered through the corrosion of feldspar and clay, and the impact of NO2 had almost no obvious effect on the microbial structure except the abundance of phylum and genus after 90 days. In addition, acid-producing bacteria appeared after 60 days, such as Bacillus, Acinetobacter, and Lactococcus, etc., lower the pH in the solution and accelerate the dissolution of minerals. The Fe (III)-reducing microbes Citrobacter freundii reduce the Fe (III) released from minerals to Fe (II) and induce siderite (FeCO3) biomineralization through biogeochemical processes. Therefore, the co-injection of trace NO2 will not significantly affect the growth of microorganisms on long timescale.

Effects of Supercritical CO2 Treatment Temperatures on Mineral Composition, Pore Structure and Functional Groups of Shale: Implications for CO2 Sequestration

Research on the physicochemical reactions between supercritical carbon dioxide (Sc-CO2) and shale at different temperature is essential for geological CO2 sequestration. In this paper, shale from the Longmaxi formation in Sichuan basin of China was collected to study the changes in mineral composition, pore structure, and organic functional groups treated with Sc-CO2 at fixed pressure 8 MPa and temperatures 40 °C to 80 °C. Samples were analyzed with x-ray diffraction, CO2/N2 gas adsorption, and Fourier transform infrared spectroscopy. The results show that the dissolution of clay minerals by Sc-CO2 first declined, but then increased when the temperature increased; dissolution reached a minimum at 60 °C. The specific surface area, total pore volume, predominant pore type (mesopores), and fractal dimension of the shale pore structure first increases and then decreases with increasing temperature. The destruction of hydroxyl structures by Sc-CO2 is related to the destruction of OH–N and ring hydroxyls. As the temperature increases, the hydroxyl destruction first increases and then decreases. The aromatic hydrocarbons are mainly dominated by 3H and 2H, and their abundances increase significantly as temperature increases, whereas the 4H shows a decreasing trend; the 1H abundance does not change appreciably. The relative abundances of aromatic and aliphatic hydrocarbons decrease linearly as the temperature increases. These research results provide theoretical support for the geological storage of Sc-CO2 in shale at different temperatures.

Numerical Modeling of Radial Fracturing of Cement Sheath Caused by Pressure Tests

To achieve an acceptable level of zonal isolation, well integrity should be guaranteed in hydrocarbon production and geological CO2 sequestration. Well pressure test can cause different types of failures in the well system leading to leakages through these failures. Laboratory evidences have revealed that occurrence of radial tensile fractures is likely during pressure tests. In this paper, we use a numerical code call MDEM which was formulated based on discrete element method. The code can model discontinuum feature of fractures. A model of a lab-sized pressure test was built and compared to an experiment previously published. The model was tested under different confinement levels and effect of the tensile strength of rock on the radial fracture was investigated at the same lab-scale. Fracture opening profiles are also presented showing the leakage potential of these fractures under different pressure level.

The application, required investments and operational costs of geological CO2 sequestration: a case study

The integrity of natural systems is already at risk because of climate change caused by the intense emissions of greenhouse gases in the atmosphere. The goal of geological carbon sequestration is to capture, transport and store CO2 in appropriate geological formations. In this review, we address the geological environments conducive to the application of CCS projects (Carbon Capture and Storage), the phases that make up these projects, and their associated investment and operating costs. Furthermore it is presented the calculations of the estimated financial profitability of different types of projects in Brazil. Using mathematical models, it can be concluded that the Roncador field presents higher gross revenue when the amount of extra oil that can be retrieved is 9.3% (US$ 48.55 billions approximately in 2018). Additional calculations show that the Paraná saline aquifer has the highest gross revenue (US$ 6.90 trillions in 2018) when compared to the Solimões (US$ 3.76 trillions approximately in 2018) and Santos saline aquifers (US$ 2.21 trillions approximately in 2018) if a CCS project were to be employed. Therefore, the proposed Carbon Capture and Storage method in this study is an important scientific contribution for reliable large-scale CO2 storage in Brazil.

Variation of Contact Angles in Brine/CO2/Mica System considering Short-Term Geological CO2 Sequestration Condition

Geological CO2 sequestration has been proposed as an effective solution to mitigate excessive human-emitted CO2 in atmosphere. Knowledge of immiscible two-phase flow of CO2-water/brine is necessary to evaluate the efficiency and safety of geological storage sites. Among forces dominating fluid flow, capillary pressure is highly important because of high uncertainty in measurement due to ambiguous wettability behavior of geomaterials. In particular, time-dependent wettability of geomaterials is of interest for predicting short-term performance of the storage site. After injection of CO2 into an aquifer, both the CO2 and water/brine in rocks pores are unsaturated and tend to dissolve into each other. Present study investigates the variation of contact angle on mica sheet using a captive bubble method at a wide range of pressures and salinities under unsaturated condition. Our results showed a general increase of contact angle with time. Comparison of unsaturated contact angle with previous results in the literature showed a wide span of wettability behavior, ranging from receding to advancing contact angle values reported in the literature. The observed decrease in wettability by time due to heterogeneity and pinning effect of triple line can jeopardize the safety of geological carbon sequestration projects in short-term after injection of CO2.